[Zope] Timeout on authenticated user?

Hi all I want to be able to timeout an authenticated user. I am planning on using a session object to store the username and set the timeout on that object. When the session object timed-out, I will see that there is no username and I can then set the authenticateduser to Anonymous. I am not quite sure how to do that (set the authenticated user to something else - is it enough just to se the REQUEST variable?) and if my methodology is good at all! Any other suggestions on tackling this? B.T.W. I am going to create a session object storing some extra info on the user anyway, that's why I thought of using the session object to do the timeouts with. Etienne